Aerodynamic power available from stall flutter of a pitching airfoil: A parametric experimental study

This experimental study investigates the available aerodynamic power from the stall flutter-induced oscillations of a National Advisory Committee for Aeronautics (NACA) 0015 airfoil. Using a one-degree-of-freedom pitching apparatus, a comprehensive parametric investigation was conducted at Reynolds numbers ranging from 6 × 104 to 1.6 × 105, exploring the influence of torsional stiffness, elastic axis location, and preset angle of attack. The available aerodynamic power was quantified and directly correlated with the topological characteristics of the pitching moment hysteresis loops. The results show that symmetric limit cycle oscillations (LCOs), which engage dynamic stall on both airfoil surfaces, generate significantly more power than asymmetric LCOs. Furthermore, hysteresis loops with three-subloop patterns, indicative of deep dynamic stall, yield more power than two-subloop patterns characteristic of light dynamic stall. Shifting the elastic axis downstream from 0.25c to 0.33c enhanced the available power by up to 107%. A key finding is the transition from asymmetric to symmetric LCOs at low preset angles, driven by increasing airspeed, which resulted in a 176% increase in available aerodynamic power.